TypeError: SourceNode.fromSourceWithMap is not a function

[tschaub]

I'm submitting a bug report

Webpack version:
2.4.1

Webpack Karma version:
2.0.3

Karma version:
1.6.0

Please tell us about your environment:
OSX 10.11.6

Browser: Chrome 57

Current behavior:

If your webpack config is an array (if mocha is "wrapped") and if you are using sourcemaps (e.g. with the devtool option), you see errors like this logged:

TypeError: SourceNode.fromSourceWithMap is not a function
    at Object.module.exports (/path/to/karma-webpack-test/node_modules/karma-webpack/lib/mocha-env-loader.js:25:29)
    at LOADER_EXECUTION (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:119:14)
    at runSyncOrAsync (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:120:4)
    at iterateNormalLoaders (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:229:2)
    at iterateNormalLoaders (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:218:10)
    at /path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:233:3
    at Object.context.callback (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:111:13)
    at Object.module.exports (/path/to/karma-webpack-test/node_modules/babel-loader/lib/index.js:172:8)
    at LOADER_EXECUTION (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:119:14)
    at runSyncOrAsync (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:120:4)
    at iterateNormalLoaders (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:229:2)
    at Array.<anonymous> (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:202:4)
    at Storage.finished (/path/to/karma-webpack-test/node_modules/enhanced-resolve/lib/CachedInputFileSystem.js:38:15)
    at /path/to/karma-webpack-test/node_modules/enhanced-resolve/lib/CachedInputFileSystem.js:69:9
    at /path/to/karma-webpack-test/node_modules/graceful-fs/graceful-fs.js:78:16
    at FSReqWrap.readFileAfterClose [as oncomplete] (fs.js:445:3)

If you are not using sourcemaps (but if you still have an array for the webpack config), you see errors like this logged:

Error: callback(): The callback was already called.
    at Object.context.callback (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:106:10)
    at Object.module.exports (/path/to/karma-webpack-test/node_modules/karma-webpack/lib/mocha-env-loader.js:42:8)
    at LOADER_EXECUTION (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:119:14)
    at runSyncOrAsync (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:120:4)
    at iterateNormalLoaders (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:229:2)
    at iterateNormalLoaders (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:218:10)
    at /path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:233:3
    at Object.context.callback (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:111:13)
    at Object.module.exports (/path/to/karma-webpack-test/node_modules/babel-loader/lib/index.js:172:8)
    at LOADER_EXECUTION (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:119:14)
    at runSyncOrAsync (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:120:4)
    at iterateNormalLoaders (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:229:2)
    at Array.<anonymous> (/path/to/karma-webpack-test/node_modules/loader-runner/lib/LoaderRunner.js:202:4)
    at Storage.finished (/path/to/karma-webpack-test/node_modules/enhanced-resolve/lib/CachedInputFileSystem.js:38:15)
    at /path/to/karma-webpack-test/node_modules/enhanced-resolve/lib/CachedInputFileSystem.js:69:9
    at /path/to/karma-webpack-test/node_modules/graceful-fs/graceful-fs.js:78:16

Expected/desired behavior:

No extra output.

Here is a gist that reproduces the issue: https://gist.github.com/tschaub/b7700159dad789c4a0b91f2038dd0f58